Challenging Sludge Logistics In Scotland

Auty, D.1 and Duff, B.2, 1Entec UK Ltd, 2Scottish Water


Scotland has many unique features, not the least of which is its sewage and sludge treatment infrastructure. This paper aims
to highlight the unique logistical difficulties faced by Scottish Water (SW) and how, in overcoming these problems there are
learning points that can be applied to all the UK water plcs.

In May of 2005, Entec were privileged to have won the contract to deliver a nationwide sludge strategy for Scottish
Water. This was a very detailed project to look at all things pertaining to sludge, one aspect of which, logistics, is
considered here.

Amongst the UK water companies, Scottish Water faces unique challenges arising from the distribution of its
population. The majority of Scots live in the 'central belt' between Glasgow and Edinburgh. Hence around 70% of the
sludge in Scotland arises in this area, with another 20% up the east coast. The remaining 10% is produced over the
remaining 80% of the land area of Scotland, mostly in 1400 septic tanks adopted by Scottish Water each typically serving
a handful of dwellings. Given the rural nature of much of Scotland and the Munros and Glens that attract the tourists,
it is clear that the tankering logistics are not simple.

This paper looks in detail at this unique distribution of works sizes and locations as well as the types of sludge assets
operated on these works (ranging from nothing to facultative lagoons) in order to set the scene for the special factors that
apply to Scottish Water's sludge tanker logistics. Next, we explore the cost of operating the tanker fleet and the many
contributory factors like tanker size distribution, %DS of sludge carried, distances travelled, average speed attainable
and distractions from the primary role of a sludge tanker (it makes a very expensive mobile pump). Clearly some of
these factors are not within the control of Scottish Water, but for some of those that are, we compare them to industry
norms. Having defined where cost savings can be made the paper will expand upon how savings are ultimately taken from
the bottom line by optimising tanker areas and routes, using larger vehicles and operating the fleet for longer hours. The
implementation of such changes requires careful planning and a number of small capital schemes to be implemented.
These will deliver best value if they are delivered in tankering management areas and co-ordinated in the form of Area
Logistics Plans.

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